In a pressure controller, a drive piston and pressure control valve are freely movably supported in a housing, the drive piston is supported by being energized and the pressure control valve is supported by being energized to make a pressure chamber and a decompression chamber communicatively connectible, the drive piston and the pressure control valve are moved by an electromagnetic force of a solenoid via a ring piston to make a hyperbaric chamber and the pressure chamber communicatively connectible and also an external piston is freely movably provided facing the drive piston and by making a control pressure acting on the external piston from a rear pressure chamber on a drive piston side equal to or greater than an external pressure acting from outside from an input unit, pressure control can properly be performed by readily moving a drive valve by pressure from outside when a power supply is defective.